The Hunter Clone was a version of the Hunter which was not developed by Umbrella Corporation. In reality, it was based on stolen samples of the original version of the Hunter (Hunter a) with some modifications to it's genetic structure as improvements. It is unknown exactly which organisation developed the clones but it is thought that
Albert Wesker was involved.
The core improvement over the 'official' version of the Hunter was that the clones were much larger and more powerful. Whereas the originals were relatively human sized, the clones were enormous in comparison and were far heavier. Their main disadvantage was that this made them slower - but not by much.
The clones were developed as a black marketable B.O.W. (Bio-Organic Weapon) on a production line and sold to interested parties. One such buyer was the Italian "Il Veltro" criminal organisation. They purchased an unspecified (but large quantity) of the Hunter Clones and stockpiled them. They were unleashed throughout the city Terragrigia, which was at one point a new bustling city on the water - it was since destroyed by the incident and the Hunter Clones absolutely had a part to play in it.
After their usefulness was over, it is thought that they were left to fend for themselves in the ruins of the city, as some time later a few evolved versions of the clones began to appear.